1. Field of the Invention
The present invention relates to a motor and a disk drive apparatus.
2. Description of the Related Art
Spindle motors arranged to rotate disks are typically installed in hard disk apparatuses and optical disk apparatuses. Such a spindle motor includes a stationary portion fixed to a housing of the apparatus, and a rotating portion arranged to rotate while supporting the disk(s). The spindle motor is arranged to produce a torque by magnetic flux generated between a stator and a magnet, whereby the rotating portion is caused to rotate with respect to the stationary portion. A known spindle motor is described, for example, in JP-A 2006-331558.
A rotating portion of the spindle motor described in JP-A 2006-331558 includes a rotor hub on which a disk is mounted, a rotor yoke, and a magnet. The rotor yoke is fixed to an inner circumferential surface of the rotor hub. In addition, an inner circumferential surface of the rotor yoke and an outer circumferential surface of the magnet are fixed to each other through adhesion or the like (see paragraph [0030] and FIG. 2 of JP-A 2006-331558).
In the case where only an upper axial end portion and its vicinity of the rotor yoke are fixed to the rotor hub in such a motor, the rotor yoke is able to have a high degree of roundness in the vicinity of the upper axial end portion thereof, but a deformation of the rotor yoke may occur, resulting in a reduced degree of roundness of the rotor yoke, in the vicinity of a lower axial end portion of the rotor yoke. The reduced degree of roundness of the rotor yoke may easily lead to a reduced degree of roundness of the magnet, which is fixed to the rotor yoke. If a reduction in the degree of roundness of the magnet occurs, a distance between the magnet and a stator becomes uneven along a circumferential direction, causing magnetic forces to be applied unevenly along the circumferential direction, which may cause vibrations of the spindle motor.